1. Field of the Invention
The present invention relates to MRI technology and, particularly, to a receiving device for an MRI system.
2. Description of the Prior Art
MRI is an imaging technology that reconstructs an image by making use of magnetic resonance signals generated due to a magnetic resonance phenomenon of an atomic nucleus in a magnetic field. The basic principle of the magnetic resonance phenomenon lies in that the proton(s) in an atomic nucleus containing a singular number of protons, for example a proton in a hydrogen atomic nucleus that exists in large amounts in a human body, would have spin motion, which carries positive charge and generates a magnetic moment, just like a magnet, in an even magnetic field its spin axis would realign according to the direction of magnetic lines, and in this case, when excited by RF (Radio Frequency) pulses at a particular frequency, the magnet would absorb a certain amount of energy and start resonance, which is referred to as the magnetic resonance phenomenon.
In an MRI system, RF coils are formed by a transmitting coil and a receiving coil, which are important for generating the abovementioned magnetic resonance phenomenon. Taking the imaging inside a human body as an example, the transmitting coil is used to transmit RF pulses at a particular frequency towards the human body to excite the hydrogen atomic nuclei, and the hydrogen atomic nuclei inside the human body receive the RF pulses so as to start the resonance. After the transmitting coil has stopped transmitting the RF pulses, the hydrogen atomic nuclei in the human body transmit magnetic resonance signals to the receiving coil. The internal image in the human body can be formed by reconstruction with the magnetic resonance signals received by the receiving coil, thus the receiving coil carries out the function of receiving the magnetic resonance signals in an MRI system, and it is the receiving device for the MRI system, and its number can be one or more than one.
FIG. 1 shows a schematic view of a singular receiving coil for receiving magnetic resonance signals in the prior art. The receiving coil 11 can only receive the magnetic resonance signals in the same direction as the Z axis perpendicular to a horizontal plane where the receiving coil itself locates, and a tangent line at every point on a magnetic line 12 and in the same direction as the magnetic line represents a sensitivity vector of the receiving coil 11, wherein the larger is the component of the sensitivity vector along Z axis, the higher is the sensitivity of the receiving coil 11 to the magnetic resonance signals at the point corresponding to the sensitivity vector, thus the higher is the imaging quality reconstructed in a reconstruction algorithm by using the magnetic resonance signals received at that point. FIG. 1 only shows one magnetic line 12 of the receiving coil 11, and taking the points p1, p2 and p3 on the magnetic line 12 as examples, the sensitivity vector H1 of the point p1 has a component in the same direction as the Z axis, and the sensitivity vector H2 of the point p2 is perpendicular to the Z axis, i.e., it has no component in the same direction as the Z axis, and the sensitivity vector H3 of the point p3 itself is parallel to the Z axis, therefore, the sensitivity of the receiving coil 11 to the magnetic resonance signal at the point p1 lies between the sensitivities at the points p2 and p3, and the sensitivity to the magnetic resonance signal at the point p2 is the poorest, and the sensitivity to magnetic resonance signal at the point p3 is the best.
According to the above analysis approach, when considering all magnetic lines of the receiving coil 11, the points similar to the point p2, whose sensitivity vectors are perpendicular to Z axis, form connection lines at the boundary of the receiving coil 11, and such lines are generally referred to as lines of strong phase variation in sensitivity, FIG. 2 shows a schematic view of the lines of strong phase variation in sensitivity of the singular receiving coil in FIG. 1, and in FIG. 2 only two lines of strong phase variation in sensitivity 21 and 22 of the singular receiving coil 11 are shown. As shown in FIG. 2, all the points of the lines of strong phase variation in sensitivity 21 and 22 of the receiving coil 11 at the boundary have the poorest sensitivity to magnetic resonance signals, leading to relatively poor imaging quality, while a sensitivity to magnetic resonance signals at the middle position of the receiving coil 11 is the best, leading to better imaging quality.
In order to increase imaging speed and to enlarge imaging area, using a number of receiving coils for receiving magnetic resonance signals in MRI has become a technology attracting a lot of attention, and has become an important development direction for the future of MRI, and one of the abovementioned techniques of using a plurality of receiving coils for receiving magnetic resonance signals is the integrated parallel acquisition technique (IPAT), and it has rapidly become a popular technique. The reconstruction imaging algorithm in IPAT technique utilizes the respective sensitivity to the magnetic resonance signals for each coil to carry out space encoding, and the quality of the sensitivities of the respective receiving coils to the magnetic resonance signals will directly affect their imaging quality. The abovementioned space encoding also has a phase encoding direction, which can also be called an imaging acceleration direction, and which are two directions perpendicular to each other in the receiving coil plane; and every time the imaging is carried out, the space encoding is performed only to the sensitivity of magnetic resonance signals of the receiving coils in the same imaging acceleration direction, therefore every time the imaging is carried out, only the receiving coils located in the imaging acceleration direction to which a current imaging is directed will affect the sensitivity of magnetic resonance signals and the imaging quality.
Taking IPAT imaging as an example, there is a junction region between adjacent receiving coils, and FIG. 3 is a schematic view of a junction region of two receiving coils in the prior art. In FIG. 3, x, y represent two imaging acceleration directions, and it can be seen that only in the x direction are there two adjacent receiving coils 31 and 32 aligned. There are two junction arrangements for the receiving coils 31 and 32, the first is that the receiving coil 31 covers over the receiving coil 32, and the second is that the receiving coil 32 covers over the receiving coil 31, and in whatever junction manner, the receiving coil 31 is not closely connected with the receiving coil 32, but there is a layer of insulation material for separation at the junction points (marked by B1 and B2 in FIG. 3). FIG. 4 shows a schematic view of the lines of strong phase variation in sensitivity of the two receiving coils in FIG. 3, and in FIG. 4 are shown the lines of strong phase variation in sensitivity of the receiving coils 31 and 32 in the abovementioned two junction manners, the upper part of a phantom is the abovementioned first junction manner, and the lower part of the phantom is the abovementioned second junction manner, wherein the size of spacing between the receiving coil 31 and the receiving coil 32 is the thickness for filling in said insulation material. Similarly to the analysis of the singular receiving coil, the boundaries of the receiving coil 31 and the receiving coil 32 are still of the poorest sensitivity to magnetic resonance signals on the lines of strong phase variation in sensitivity, and since the junction region of abovementioned receiving coils 31 and 32 is formed by the boundaries of the receiving coils and the two receiving coils are located in the imaging acceleration direction x, the problem of relatively poor imaging quality when directing to the x direction also exists.
Therefore, although this manner of using multiple receiving coils to perform MRI can increase the imaging speed and extend the imaging area, there also exists the problem of relatively poor imaging quality in the junction region of adjacent receiving coils in the imaging acceleration direction to which the imaging directs, thus affecting the overall imaging quality.